In an energy-assisted magnetic recording (EAMR) system (e.g., hard disk), the minimum written bit size in the media is controlled by the minimum optical spot size produced by a near field transducer (NFT) acting as a plasmon element. In one design, the NFT has two portions, such as a disc and a pin, that serve different purposes. The disc converts electromagnetic energy of incident light into surface plasmons, and the pin channels a highly localized surface plasmon field to an air bearing surface (ABS). The performance of the NFT, both electric field intensity and spot size, depends on a number of NFT parameters such as core-NFT spacing, NFT-spacer interface, NFT size, NFT shape, NFT thickness, pin length, pin width, pin thickness, and NFT material. Additionally, the performance depends on the illumination conditions which are determined by the waveguide geometry (e.g., solid immersion minor or channel waveguide) and grating coupler design.
In the related art, device characterization is generally performed at bar or slider level. However, bar or slider level testing can be time consuming and expensive processes because they involve many backend processes (e.g., lapping process and other processes). In other related art, device characterization is attempted using a single disk NFT or multiple disk NFTs configured to interact with a conventional waveguide mode, or using a pump probe system for testing a single NFT on a wafer. However, both approaches exhibit shortcomings including poor signal to noise ratio and generally poor device characterization capabilities that make it difficult to draw conclusions from the test data. Therefore, it is desirable to develop improved systems and methods to characterize the performance of a wafer level NFT such that the testing and development cycles can be reduced.